1. Technical Field
The present invention relates to a wavelength variable interference filter, a manufacturing method of a wavelength variable interference filter, an optical filter device, an optical module, and an electronic apparatus.
2. Related Art
In the related art, there has been known a wavelength variable interference filter in which reflection films are disposed to oppose each other on surfaces of a pair of substrates which oppose each other (for example, see JP-A-2011-197386).
The wavelength variable interference filter disclosed in JP-A-2011-197386 is a wavelength variable interference filter obtained by joining a lower substrate and an upper substrate to each other. A lower mirror is provided on a surface of the lower substrate opposing the upper substrate, and an upper mirror opposing the lower mirror is provided on a surface of the upper substrate opposing the lower substrate.
In addition, in the upper substrate, a diaphragm is provided in a region surrounding the upper mirror, in a plan view, and by displacing the diaphragm in a vertical direction, a dimension between the lower mirror and the upper mirror is displaced.
Herein, the diaphragm is obtained by performing wet etching on the upper substrate to form a groove.
However, in the wavelength variable interference filter using light of a visible light region as a target, glass through which light in the visible light region can be transmitted is generally used as the lower substrate and the upper substrate. In a case of forming the diaphragm by performing wet etching on such a glass-made upper substrate, as shown in FIG. 17, a mask M9 including an opening according to a shape of the diaphragm is used. In this case, by performing isotropic etching, the etching is performed not only in a depth direction, but also in a lateral direction from a mask opening end M91, and a side surface 926A which is formed of an arc-like curved surface around the mask opening end M91 is formed from a groove bottom surface 926B of the diaphragm to an upper surface (surface on which the mask is formed) of the upper substrate 92. Accordingly, there is a problem with the increase in size of the wavelength variable interference filter, for a size of a region D9 of the side surface 926A which is expanded further than the opening of the mask M9 in the lateral direction.